Physics
Time of exposure required for taking photograph of an object depends upon the

Brightness of the object
Proximity of object
Skill of photographer
Size of the object

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Physics
Skating on ice is possible because

The pressure on the ice due to skate melts the ice by lowering its melting point forming a thin film of water
The surface of ice is smooth
The pressure on the ice due to skate raises its melting point
Ice is cold

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